The present invention relates to an anode assembly of a magnetron and a method of manufacturing the same.
An anode assembly of a magnetron conventionally has an anode cylinder and a plurality of anode vanes radially fixed to the inner surface of the anode cylinder. Every other vanes are electrically short-circuited by a pair of strap rings. The anode assembly having this structure is manufactured in the following manner. First, a plurality of copper anode vanes are positioned within a copper anode cylinder by a couple of positioning jigs. Subsequently, silver solders are provided at connecting portions of the anode cylinder and the vanes, and the anode cylinder and the vanes are placed in a high-temperature furnace for a predetermined period of time so that they are soldered with each other.
When an anode assembly is manufactured in accordance with the above procedure, a couple of positioning jigs to be placed in a furnace together with the anode cylinder and the vanes are inevitably required for every anode assembly. As a result, when, e.g., magnetrons for electronic ovens are mass-produced on a large scale, a large number of jigs are required, resulting in high facility costs. Inversely, when the number of jigs is small, the manufacturing efficiency is decreased. The positioning jig is heated to about 900.degree. C. together with an anode assembly. Therefore, the jig must be formed of a material which is durable against repeated use at high temperatures, has small changes in size, and has a small thermal expansion coefficient. A jig satisfying these conditions is expensive and can be easily worn. A positioning jig generally has vane mount grooves. Each groove is formed to have a larger width than the thickness of the vane to allow easy mounting of the anode vane and in consideration of the thermal expansion of the jig and the vane in the soldering step. Therefore, even when the positioning jig is used, the positional relationship between adjacent vanes and, more specifically, the gap between distal end portions of the adjacent vanes which influences the high-frequency characteristics of the resonant cavity most cannot be set with high precision.
Japanese Patent Publication No. 57-18664 discloses a manufacturing method wherein an anode assembly is soldered in the soldering step without using a positioning jig. According to this manufacturing method, the connecting portions of the vanes and the anode cylinder are preliminarily fixed by welding prior to soldering of the vanes to the anode cylinder. Thereafter, these constituent components are soldered without using a jig. This manufacturing method can eliminate the drawbacks described above. However, when preliminary fixing is performed by, e.g., laser welding, welding with high bonding strength cannot be achieved since both the anode cylinder and vane are made of copper having a considerably high thermal conductivity. In addition, thermal strain tends to locally occur at the connecting portions during welding, and the gap between the adjacent vanes cannot always be set with high precision. The above manufacturing method thus still poses a problem to be solved.